题目描述

从上到下打印出二叉树的每个节点，同一层的节点按照从左到右的顺序打印。

https://leetcode.cn/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/

题解

层序遍历

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class Solution {
public:
    vector<int> levelOrder(TreeNode* root) {
        if (!root) return {};
        vector<int> res;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            TreeNode* node = q.front(); q.pop();
            if (node->left) q.push(node->left);
            if (node->right) q.push(node->right);
            res.push_back(node->val);
        }
        return res;
    }
};

时间复杂度 O(n)，空间复杂度 O(n)